This invention relates to vehicle seats having a basic support frame and an additional frame supported by the basic support frame. German Offenlegungsschrift No. 44 21 946 and Published International Application No. WO 95/11 818 describe in detail the hazards to which vehicle occupants are exposed in the event of a rear impact.
To reduce the risk of injury to passengers, German Offenlegungsschrift No. 44 21 946 discloses a seat having cross-connections within a backrest framework which can be deformed in their longitudinal direction in an energy-absorbing manner. This arrangement is intended to permit the occupant of the seat to plunge into the backrest by a predetermined amount in the event of a rear impact. The disadvantage of this arrangement, however, is that the permissible plunging movement is restricted to the pelvic region of the occupant. There is no comparable arrangement for the occupant's shoulder region. This problem is addressed in the PTO published application No. WO 95/11 818. In this arrangement, cross-strips are provided which are designed as breaking elements to break when a predetermined force is exceeded, producing a cushion spring arrangement which can be elastically displaced rearwardly. The seat occupant can thus plunge in the direction of the backrest in both the pelvic region and the shoulder region. In addition, this document describes a support element supporting the cushion spring arrangement that can be pivoted as a function of signals from a crash sensor about an axis extending at pelvis height so that backward displacement of the vehicle occupant relative to the backrest frame causes the occupant's head to be guided onto the head restraint. Sudden release of the support element, however, results in an increased impact load in the shoulder region of the vehicle occupant.
German Patent No. 42 38 549 describes a backrest frame with backrest side parts which have an energy-absorbing construction. No protective measures for the shoulder and/or pelvic region are provided.
German Gebrauchsmuster No. 91 03 611.9 shows a seat arrangement having a seat support which is mounted by a spring mounting in a floating manner in a seat framework. The floating mounting is arranged so that, for normal driving operations, the driver is comfortably accommodated in the most diverse terrain conditions.
German Gebrauchsmuster No. 92 15 254 shows a seat framework having floor-mounted legs of energy-absorbing construction. When the seat is subjected to a load, it tips forward.